Mining ventilation method

ABSTRACT

There is disclosed a method for mining relatively thick mineral seams comprising removing seam material adjacent the seam top in an advancing direction to form a passage in the seam and then removing seam material from the passage floor in a retreating direction.

United States Patent Thompson 1 Oct. 3, 1972 54] MINING VENTILATION METHOD [72] lnventor: Cullen R. Thompson, Denver, Colo.

[73] Assignee: Shell Oil Company, New York, NY.

[22] Filed: Oct. 16, 1970 [211 App]. No.: 81,302

2,651,513 9/1953 Ramsay ..299/11 3,167,354 l/ 1965 Macaul et al. ..299/1 1 1,622,837 3/1927 Pearce ..299/19 X FOREIGN PATENTS OR APPLICATIONS 193,407 7/ l967 U.S.S.R. ..299/80 Primary Examiner-Emest R. Purser Attorney-Harold L. Denkler and Theodore E. Bieber [57] ABSTRACT There is disclosed a method for mining relatively thick mineral seams comprising removing seam material adjacent the seam top in an advancing direction to form a passage in the seam and then removing seam material from the passage floor in a retreating direction.

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MINING VENTILATION METHOD BACKGROUND OF THE INVENTION Two common methods of mining minerals are known as strip and underground mining. Strip mining is particularly applicable when the mineral to be excavated is fairly close to the surface. The overburden is stripped away with suitable excavating machines to expose a substantial part of the mineral seam. The mineral is then removed by suitable excavating machines as is well known and commonly practiced. A major advantage of strip mining is high productivity. With the present state of the art in stripping coal for example, productivities of 60 tons per man-day are not uncommon. The economic limit of a strip mining operation is determined in large part by the amount of overburden that must be handled to expose a unit of ore.

Underground mining techniques are customarily used to remove ore from seams which are buried to such an extent that the cost of removing overburden is prohibitive. The productivity of underground mining operations is likewise increasing but does not now approach the productivity obtained in strip mining operations. In the present state of the art in the coal industry, 30 tons of coal per manday is considered excellent. There are other disadvantages of underground mining which are expensive and difficult to overcome. These include ventilation problems, roof support, drainage and the like.

Although the present invention is applicable for mining any type of mineral existing in a relatively thick seam, it has immediate application in the coal industry to which further background discussion will be limited. Most underground coal mining conducted in the United States is in the East and Midwest in close proximity to markets. The buried coal seams in these areas tend to be rather thin, usually on the order of IS feet or substantially less. Consequently, present day underground mining equipment has evolved over many years to efficiently mine thin seams.

Much of the coal produced in the eastern and midwestern sections of the United States has substantial sulphur and ash content. Widely evidenced concern about air pollution has stimulated the search for coal reserves having low sulphur and ash content. Such coal reserves have been located in the western United States and are typically found in relatively thick nearly horizontal seams. Erosion processes in the coal bearing areas have formed valleys in which the coal seams are exposed. The same coal seam may often be found on opposite sides of a mountain leading to the logical conclusion that the coal bed extends under the mountain. It will be apparent to those skilled in the art that strip mining operations on the side of the mountain becomes uneconomical since the overburden progressively increases in thickness. Removing the entire mountain to expose the coal seam is, upon the most rudimentary examination, uneconomical. As the strip mining operation approaches the economic limit, the only course of action open to the operator with the present state of the art is to utilize the underground mining equipment and techniques developed for mining thin seams. It will be apparent that using equipment and techniques which are capable of mining foot thick seams leaves a substantial quantity of coal in the ground when the seam is, for example, 80 feet thick. It is accordingly desirable to develop techniques for mining thick mineral seams which are covered with sufficient overburden to prevent economic strip mining operations.

SUMMARY OF THE INVENTION It is an object of the invention to provide a method of mining a significant portion of a thick mineral seam substantially covered with overburden of considerable thickness.

Another object of the invention is to provide a method to continue mining a thick mineral seam which is progressively covered by thicker overburden following a strip mining operation.

The method of this invention comprises mining a mineral seam substantially covered with overburden and having a portion exposed for access comprising the steps of removing material from adjacent the top of the seam to form a passage therealong extending away from the exposed portion under the overburden and then removing seam material from the around the passage sequentially from a position away from the exposed portion through positions successively closer to the exposed portion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart summarizing the mining method of this invention;

FIG. 2 is a cross sectional view of a mine illustrating the excavation of a tunnel adjacent the seam top while advancing into the seam;

FIG. 3 is a view similar to FIG. 2 illustrating the mining operation where the tunnel floor is excavated during retreat from the seam;

FIG. 4 is a view similar to FIG. 3 illustrating the use of a different type excavating device; and

FIG. 5 is a view similar to FIGS. 3 and 4 illustrating another form of excavating device which may be used to mine the tunnel floor.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, it will be seen that the method of this invention comprises excavating a tunnel adjacent the seam top while advancing into the seam and then mining'the tunnel floor while retreating from the seam. FIG. 2 illustrates the tunnel excavating step while FIGS. 3-5 disclose various approaches for mining the tunnel floor.

Referring to FIG. 2, there is shown a mineral seam 10 which may be coal or any other valuable mineral. The seam 10 is of substantial thickness and may typically be between 40 and feet thick. The seam 10 includes a top 12 and a bottom 14 which are juxtaposed to overlying and underlying strata 16, 18 respectively. The overlying strata 16 is typically called the overburden.

The seam 10 is typically exposed on the side of a mountain or bluff, the original position of which is illustrated by a phantom line 20 in FIG. 2. The seam 10 may be initially strip mined by removing the overburden 16 to expose the seam 10. After the strip mining operation proceeds into the side of the mountain, the economic limit is reached since the thickness of the overburden soon reaches substantial proportions as will be apparent to those skilled in the art. It will be apparent that the operator of such a seam is faced with undesirable alternatives based on the existing state of the art.

In the practice of this invention, a tunnel or passage 22 is excavated into the seam adjacent the top 12 thereof extending away from the exposed face 24 of the seam 10 under the overburden 16. The tunnel 22 may be excavated in any suitable manner, as by the use of a conventional boring machine 26 having a cutting head 28 equipped with a plurality of cutting elements 30. The boring machine 26 is preferably provided with rearwardly extending conveyor means 32 receiving material from the cutting head 28 and transporting the same to the tunnel entrance. The tunnel 22 preferably extends wholly within the seam 10 rather than partially or wholly in the overburden 16 to obtain a salable product during the formation of the tunnel 22. It will be apparent that some considerations, e.g., the bearing strength of the overburden 16, may dictate cutting the tunnel 22 partially or wholly in the overburden 16. In any event the tunnel 22 is excavated for a substantial distance under the overburden 16.

The tunnel 22 formed by a conventional boring machine 26 is generally cylindrical and includes a tunnel top 34 and a tunnel floor 36. The tunnel 22 may be formed in other convenient manners as will be apparent, including the use of a continuous mining machine.

FlG. 3 represents a more advanced stage in the mining of the seam 10. After the tunnel 22 has been excavated a predetermined distance into the seam 10, the boring machine 26 is removed and a dragline 38 driven into the tunnel 22 to the end thereof. The dragline 38 includes a bucket 40 manipulated by conventional cables or flexible lines 42, 44 in conjunction with a short mast 46 pivotally mounted as at 48 to the upper works 50 of the dragline 38. Conveyor means 52 preferably extend from adjacent the dragline 38 through the tunnel 22 to the entrance thereof for conveying seam material toward the surface. The conveyor means 52 preferably extends between the tracks of the dragline 38 so that the bucket 40 may be dumped immediately in front of the upper works 50 onto the end of the conveyor means 52.

After the dragline 58 has made a cut 54 to adjacent the seam bottom 14, a ventilation conduit 56 is installed adjacent the innermost end of the tunnel 22. The conduit 56 may be installed by positioning a drilling rig on the mountain side above the tunnel 22 and drilling a borehole 58 through the overburden 16 into the tunnel 22. The ventilation conduit 56 may be run into the borehole 58 from the surface and affixed in place, as by typical oil field procedures. To this end, the borehole 58 may penetrate the underlying strata 18 to receive the conduit 56. After the drilling rig is removed, exhaust fans and other ventilation equipment may be connected to the conduit 56 to draw air through a plurality of apertures 60 extending from adjacent the tunnel top 34 to adjacent the bottom of the cut 54.

It will accordingly be seen that air enters the tunnel 22 adjacent the exposed face 24, passes through the tunnel 22 past the dragline 38 and then through the cut 54 to exit through the conduit 56. It will be seen that air passing through the tunnel 22 is first delivered to workmen in the dragline 38 and then passes through the cut 54. This ensures that relatively fresh dust-free air is delivered to the workmen while gases evolving from broken material in the cut 54 is swept into the ventilation conduit 56.

The dragline 38 continues to mine the floor of the tunnel 22 while retreating out of the seam 10. In the terminal stages of mining the tunnel floor 36, the dragline 38 may back out of the tunnel 22 and down the exposed face 24, removing seam material so long as it is economical. It will be seen that a slot has been cut into the seam 10 from which the seam material has been removed. To continue mining the seam 10, the boring machine 26 is positioned laterally of the depleted slot and a new tunnel is bored. The spacing between tunnels is dependent upon bearing strength of the seam material 10 and other parameters as will be apparent to those skilled in the art.

The mining method of this invention provides several major advantages. The first is the capability of removing a significant proportion of seam material from a seam of substantial thickness. Another important advantage is that the productivity of the disclosed mining operation approaches the high productivity of strip mining. Also important is the direction of air circulation which presents relatively fresh air to men working in the mine and which sweeps mine gases and dust away from the workmen and equipment. Another feature of this mode of air circulation is that air velocity in the tunnel 22 is substantially greater than air velocity in the cut 54 as a result of the difference in cross sectional area thereof. Accordingly, any gas seepage from the seam 10 into the tunnel 22 is immediately swept into the cut 54 thereby preventing the accumulation of hazardous mine gases in the vicinity of the dragline 38. Another important feature is that the workmen and mining machinery are continually retreating from the high ceiling in the cut 54. Since roof falls are much more dangerous in the area of the high ceiling afforded by the cut 54 it will be apparent that the method of this invention minimizes danger to men and equipment conducting the mining operation. Since roof failure and impure air are major hazards in underground mining operations, it will be seen that the method of this invention allows the workmen to continually retreat from the area of greatest danger.

Referring to FIG. 4, there is shown another means of mining the tunnel floor while retreating from the ore seam. An ore seam 62 having a top 64 and a bottom 66 has been bored to form a tunnel 68 thereinto. The tunnel 68 includes a roof 70 and a floor 72 and extends away from an exposed face 74 of the seam 62. An overlying strata 76 comprises the overburden while a strata 78 underlies the ore seam 62.

After the tunnel 68 has been cut a predetermined distance into the seam 62, a trenching machine 80 is moved into the tunnel 68 adjacent the end thereof. The trenching machine 80 comprises a pair of endless crawlers 82 carrying a chassis 84 on which is located an operators cab 86 and an engine compartment 88. An elongate boom 90 is pivoted to the forward end of the chassis 84, as at 92 and carries a plurality of buckets 94 which are driven by an endless member, such as a chain. Suitable means (not shown) are provided to elevate and depress the boom 90 about the pivot axis 92 to position the buckets 94 adjacent the seam 62. Movement of the buckets 94 about the boom 90 operates to deliver seam material to a conveyor 96 extending beneath the trenching machine 80 through the tunnel 68 toward the entrance thereof.

After a cut 98 has been excavated in the tunnel floor 72, a ventilation conduit 100 having apertures 102 therein is installed. Retreat of the trenching machine 80 from the seam 62 excavates material from the seam 62 for delivery by the conveyor 96 to the tunnel entrance. Operation of ventilation equipment, such as exhaust fans and the like attached to the conduit 100, causes air circulation through the tunnel 68. The direction of air circulation is through the tunnel 68 and past the operators cab 86 into the cut 98 for exhaust through the ventilation conduit 100. It will be seen that all of the advantages accruing to the method of this invention are achieved by the use of the trenching machine 80. It will be apparent to those skilled in the art that the trenching machine 80 may be more desirable in seams of lesser thickness while the dragline 38 may be more desirable in thicker seams. In any event, it will be noted that the tunnel 68 is of a height substantially less than the thickness of the ore seam 62.

Referring to FIG. 5, there is shown another means of mining the tunnel floor while retreating from the ore seam. An ore seam 104 having a top and bottom 106, 108 and an exposed face 110 overlies a strata 112 and underlies a strata l 14. The tunnel l 16 has been cut into the seam 104 beneath the overburden 114 and includes a tunnel roof 118 and a tunnel floor 120. A ventilation conduit 122 having a plurality of apertures 124 therein is installed through the tunnel 116 adjacent the end thereof either before or after one or more inclined holes 126 are bored by an auger device 128 in the passage floor 120. lt will be apparent that the direction of air circulation remains the same.

The auger device 128 includes a chassis 130 supported by suitable ground engaging elements 132, a plurality of side-by-side augers 134 and means 136 manipulating the augers 134. The augers 134 may be of any suitable type, as now used in mining a vertical ore face. The augers 134 may be arranged to bore passages extending radially outwardly from the axis of tunnel l 16.

The manipulating means 136 is illustrated as comprising a plurality of articulated links 138, 140, 142 which may be connected by suitable hydraulic motors (not shown) for advancing the augers 134 into the seam 104 and for retracting the augers 134 to drill a new set of inclined holes 126. As the holes 126 are being excavated, seam material is removed upwardly by the augers 134 and placed on a conveyor 144 extending under the chassis 130 along the tunnel floor 120 to convey the removed seam material to the surface.

It will be seen that the use of the auger device 128 provides many of the advantages heretofore mentioned. The direction of air circulation is favorable to provide fresh air to workmen operating the device 128. Mining the tunnel floor 120 in the retreat direction allows the device 128 to retreat from the area of most damaging roof falls. Although the device 128 does not remove substantially all of the seam material between the tunnel floor 120 and the seam bottom 108, it does remove a considerable part thereof. The device 128, much like the trenching machine 80, is particularly adapted for seams of moderate thickness.

It will accordingly be seen that the mining method of this invention provides an efficient and safe means of extracting minerals from thick buried seams.

claim as my invention:

1. The method of mining a mineral seam substantially covered with overburden and having a portion exposed for access comprising the steps of:

removing material from adjacent the top of the seam to form a passage therealong extending away from the exposed portion under the overburden;

installing exhaust equipment in the passage away from the entrance thereof; removing seam material from around the passage sequentially from a position away from the exposed portion but between the exposed portion and the exhaust equipment through positions successively closer to the exposed portion; and

circulating air through the passage entrance, past the seam material removing location and into the exhaust equipment.

2. The method of claim 1 wherein the seam is buried and is exposed on an inclined portion of the surface.

3. The method of claim 1 wherein the first material removal step comprises removing seam material.

4. The method of claim 3 wherein the first seam material removing step comprises removing seam material from below the seam top.

5. The method of claim 1 wherein the seam material removing step comprises excavating seam material from the passage floor and conveying the removed seam material through the passage toward the exposed portion.

6. The method of claim 5 wherein the excavating step comprises boring a plurality of holes in the passage floor.

7. The method of claim 5 wherein the excavating step comprises boring a plurality of similarly inclined holes in the passage floor.

8. The method of claim 5 wherein the excavating step comprises excavating substantially all the seam material from the passage floor to the seam bottom.

9. The method of claim 8 wherein the excavating step comprises engaging the passage floor with at least one bucket and drawing the bucket generally toward the passage entrance.

10. The method of mining a relatively thick mineral seam substantially covered with overburden comprising the steps of removing seam material adjacent the seam top in an advancing direction forming a passage under the overburden of a height substantially less than the thickness of the seam;

installing exhaust equipment in the passage away from the entrance thereof;

removing seam material from the passage floor in a retreating direction beginning at a location between the passage entrance and the exhaust equipment; and

circulating air through the passage entrance, past the seam material removing location and into the exhaust equipment. 

1. The method of mining a mineral seam substantially covered with overburden and having a portion exposed for access comprising the steps of: removing material from adjacent the top of the seam to form a passage therealong extending away from the exposed portion under the overburden; installing exhaust equipment in the passage away from the entrance thereof; removing seam material from around the passage sequentially from a position away from the exposed portion but between the exposed portion and the exhaust equipment through positions successively closer to the exposed portion; and circulating air through the passage entrance, past the seam material removing location and into the exhaust equipment.
 2. The method of claim 1 wherein the seam is buried and is exposed on an inclined portion of the surface.
 3. The method of claim 1 wherein the first material removal step comprises removing seam material.
 4. The method of claim 3 wherein the first seam material removing step comprises removing seam material from below the seam top.
 5. The method of claim 1 wherein the seam material removing step comprises excavating seam material from the passage floor and conveying the removed seam material through the passage toward the exposed portion.
 6. The method of claim 5 wherein the excavating step comprises boring a plurality of holes in the passage floor.
 7. The method of claim 5 wherein the excavating step comprises boring a plurality of similarly inclined holes in the passage floor.
 8. The method of claim 5 wherein the excavating step comprises excavating substantially all the seam material from the passage floor to the seam bottom.
 9. The method of claim 8 wherein the excavating step comprises engaging the passage floor with at least one bucket and drawing the bucket generally toward the passage entrance.
 10. The method of mining a relatively thick mineral seam substantially covered with overburden comprising the steps of removing seam material adjacent the seam top in an advancing direction forming a passage under the overburden of a height substantially less than the thickness of the seam; installing exhaust equipment in the passage away from the entrance thereof; removing seam material from the passage floor in a retreating direction beginning at a location between the passage entrance and the exhaust equipment; and circulating air through the passage entrance, past The seam material removing location and into the exhaust equipment. 